Hi, I understand the problem your facing.
Short Answer: You can't fix the issue anymore
Long Answer: Around February 2017, I was able to use Ansys 17.2 plug-in in Inventor 2017 by using the Ansys CAD Configuration Manager. But later the same year around October 2017, I tried the same thing with Inventor 2018 and Ansys 18.2. It didn't work. There wasn't even a CAD configuration manager in Ansys 18.2.
I followed this thread: https://studentcommunity.ansys.com/thread/cad-configuration-manager-not-installed/
In this thread, it was revealed that the CAD integration Option has been withdrawn for the student version of the software, so you'll no longer be able to use the plug-in feature. The option is available only in Commercial License Ones, the kind used by Companies.
The only suggestion I found was to create a CAD Model->export in .iges format -> import to SpaceClaim and then make all edits in SpaceClaim.
If you or anyone else reading this thread comes across a way to get the cad integration please post it here.